Fluid mixing apparatus

ABSTRACT

A mixer apparatus for use with a vessel centered about a longitudinal axis is disclosed. The mixer has a blade body is formed along a central head axis. The blade body has a first end, a second end spaced from the first end along the head axis, and a passageway extending between the first and second ends. The passageway tapers from the first end to the second end. The outer surface of the blade body defines an inside blade diameter “ID” at the second end and an outside blade diameter “OD” at the first end. The blade body is positioned within and coaxial to the vessel. A scotch yoke, operatively connected to the blade body by a shaft, effects reciprocating longitudinal movement of the blade body through a stroke “S”, with a duration “T” for each stroke. Enhanced mixing efficiencies are achieved when the mixer is operated within a set of operational parameters defined by the equation: 80≦0.36×OD 2 /ID 2 ×S/T≦550, when OD, ID and S are expressed in inches, and T is expressed in minutes.

FIELD OF THE INVENTION

The present invention generally relates to the field of mineral oreprocessing, and more particularly, to a mixing apparatus and to usesthereof in the separation of minerals from mineral-bearing ores.

BACKGROUND OF THE INVENTION

Processes are known in the prior art which provide for the separation ofminerals from mineral-bearing ores.

For example, in known processes used for the separation of copper fromcopper-bearing ores, illustrated diagrammatically in FIG. 1,non-oxidized ores 20 (which might contain as little as 0.5% copper, andtypically contain iron sulfides) are processed in a crusher 22, withwater 24, to form a slurry 26. The slurry 26 is then transferred to aflotation cell 28, and subjected to physical action, specifically, airsparging and mixing. As a result of the physical action, a substantialportion of the copper value in the slurry 26 rises to the surface of theflotation cell 28 as a froth 30, and is skimmed therefrom by a paddlemechanism 32, while the waste rock 33 (“gangue”) remains in the bulk,and is ultimately passed from the cell 28 to a dryer 34 and dischargedas tailings 36. This process of “froth separation” results fromdifferences in wettability of copper as compared to other minerals, andis typically aided by chemical frothing and collector agents 38 added tothe slurry 26, such that the froth 30 from such flotation contains 27%to 36% copper. Methylisobutyl carbonal (MIBC) is a typical frothingagent, and sodium xanthate, fuel oil, and VS M8 (a proprietaryformulation) are typical collector agents.

The froth 30 is then fed to an oxygen smelter 40, and the copper andiron sulfides are oxidized at high temperature resulting in impuremolten metal 42 (97%-99%, copper, with significant amounts of ironoxide) and gaseous sulfur dioxide 44. The impure metal 42 is thentransferred to an electrolytic purification unit 46, which separates theimpure metal 42 into 99.99% purity copper material 48 and slag 50.

The gaseous sulfur dioxide 44 is collected in a reactor 52 wherein it isscrubbed and mixed with water 24 to form sulphuric acid 54. Thesulphuric acid 54 is suitably blended with water 24 and used to leachoxidized ores, typically by “heap leaching” an ore pile 56. Theresultant copper-bearing acid 58 is known as “pregnant leach solution”.Pregnant leach solution 58 is also obtained by mixing solutions ofsulphuric acid 54, in vats 60, with the tailings 36 discharged fromflotation operations, to dissolve the trace amounts of copper remainingtherein.

The copper is “extracted” from the pregnant leachate 58 by mixingtherewith, in a primary extraction step 62, organic solvent 64 (oftenkerosene) in which copper metal preferentially dissolves. Organicchemical chelators 66, which bind solubilized copper but not impuritymetals, such as iron, are also often provided with the organic solvent,to further drive the migration of copper. Hydroxyoximes are exemplary inthis regard.

In the primary extraction step 62, the copper is preferentiallyextracted into the organic phase according to the formula:[CuSO₄]_(aqueous)+[2 HR]_(organic)→[CuR₂]_(organic)+[H₂SO₄]_(aqueous)

where HR=copper extractant (chelator)

The mixed phases are permitted to separate, into a copper-laden organicsolvent 68 and a depleted leachate 70.

The depleted leachate 70 is then contacted with additional organicsolvent 72 in a secondary extraction step 74, in the manner previouslydiscussed, and allowed to settle, whereupon the phases separate into alightly-loaded organic (which is recycled as solvent 64 in the primaryextraction step) and a barren leachate or raffinate 76.

The barren leachate 76 is delivered to a coalescer 78 to removetherefrom entrained organics 80, which are recycled into the system; thethus-conditioned leachate 82 is then suitable for recycling into theleaching system.

The pregnant organic mixture 68 (produced in the primary extraction step62) is stripped of its copper in a stripping operation 84 by theaddition of an aqueous stripping solution of higher acidity 86 (toreverse the previous equation); after phase separation, a loadedelectrolytic solution 88 (“rich electrolyte”) remains, as well as anorganic solvent, the latter being recycled as solvent 72 in thesecondary extraction 74.

The rich electrolyte 88 is directed to an electrowinning unit 90.Electrowinning consists of the plating of solubilized copper onto thecathode and the evolution of oxygen at the anode. The chemical reactionsinvolved with these processes are shown belowCathode: CuSO₄+2e¹⁻

Cu+SO₄ ²⁻Anode: H₂O

2H⁺+0.5O₂+2e¹⁻

This process results in copper metal 92, and a lean (copper-poor)electrolyte, which is recycled as stripping solution 86.

The combination of leaching, combined with extraction andelectrowinning, is commonly known in the art as solvent extractionelectrowinning, hereinafter referred to in this specification and in theclaims as “SXEW”.

In a known application of the described SXEW process, in both theprimary 62 and secondary 74 extraction steps, the combined organic andaqueous phases are delivered through a series of mixing vessels (primaryP, second S and tertiary T), and then to a settling tank ST, the primarymixing vessel P being about 8 feet in diameter and 12 feet in height,and stirred by a rotary mixer driven by a 20 horsepower motor, and eachof the secondary S and tertiary T mixing vessels being about 12 feet indiameter and height, and stirred by a rotary mixer driven by a 7.5horsepower motor. (The system of primary P, secondary S and tertiary Tmixers, and settling tank ST, is replicated to meet volume flowrequirements, with each system processing about 10,000 gpm). Thisprovides a mixing regime wherein the organic and aqueous phases areintimately mixed for a period of time sufficient to allow copperexchange (to maximize copper recovery), yet relatively quickly separatesubstantially into organic and aqueous phases.

In a known application of the froth flotation process, a plurality offlotation cells 28, each being approximately 5 feet square and 4 feethigh, are utilized, with pairs of cells sharing a 50 horsepower motordriving respecting rotary mixers (not shown). This provides a mixingregime sufficient to allow the air bubbles to carry the copper value tothe surface.

Various modifications can be made to the rotary mixers in the extractorsand in the flotation tanks of the foregoing process. However, thegeneral configurations noted above have been found to provide relativelyeconomical results, and significant variations therefrom can impactadversely upon economies. For example, an attempt to reduce energy costsby scaling-down the motors for the mixers would have consequent impactseither upon the copper recovery efficiency, or upon available processthroughputs. Specifically, the relatively large motors employed arerequired to drive the sturdy (and therefore heavy) rotary mixers andshafts that are needed to withstand the torques caused by rotation;lower power motors would demand either lower blade speed or smallerblades, with consequent impacts upon mixing and transfer efficiency.

SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided an apparatusfor mixing fluids within a vessel having a contiguous sidewall centeredabout and defining a longitudinal axis. The mixing apparatus includes amixing head, means for mounting the mixing head within the vessel, andmeans for imparting reciprocating longitudinal movement to the mixinghead. The mixing head has a blade body for immersion in the fluids. Theblade body has a first end, an opposed second end disposed in spacedrelation thereto along a blade body axis, and a passageway extendingtherealong between the first and second ends. The passageway tapers fromthe first end to the second end. The blade body further has an innersurface and an outer surface. The outer surface of the blade bodydefines an inside blade diameter ID at the second end, and an outsideblade diameter OD at the first end. The reciprocating longitudinalmovement imparted to the mixing head is defined by a stroke length S,with a duration T for each cycle. The mixing apparatus is operablewithin a set of operational parameters defined by the equation:80≲0.36×OD ² /ID ² ×S/T≲550,where OD, ID and S are each expressed in inches, and T is expressed inminutes. By virtue of the reciprocating longitudinal movement impartedto the mixing head, a portion of the fluids is urged to flow through thepassageway defined in the blade body to thereby encourage efficientmixing of the fluids in the vessel.

In an additional feature, the stroke length S is between 2 inches and 24inches. Preferably, the stroke length S is between 4 inches and 16inches. More preferably, the stroke length S is between 8 inches and 12inches.

In a further additional feature, the OD:ID is greater than 1.0 and lessthan or equal to 1.7. Preferably, the OD:ID is between 1.5 and 1.7. Inyet another feature, the stroke length S is between 8 and 12 inches; andthe OD:IB is between 1.5 and 1.7.

In another aspect of the invention, there is provided an apparatus formixing fluids within a vessel having a contiguous sidewall centeredabout and defining a longitudinal axis. The mixing apparatus includes ahousing, a mixing head, a shaft, a reciprocating drive assembly, and alinear bearing assembly. The housing is positionable above said vessel.The mixing head has a blade body for immersion in the fluids. The bladebody has a first end, an opposed second end disposed in spaced relationthereto along a blade body axis, and a passageway extending therealongbetween the first and second ends. The passageway tapers from the firstend to the second end. The shaft for supporting the mixing head andextends into the vessel. The reciprocating drive assembly is positionedsubstantially within the housing. The reciprocating drive assembly isoperatively connected to the shaft to impart reciprocating longitudinalmovement to the mixing head. The linear bearing assembly is mounted tothe housing in surrounding relation to the shaft. The linear bearingassembly includes upper and lower bearing subassemblies for engagementwith the shaft at respective upper and lower, longitudinally spaced,locations.

In an additional feature, the upper bearing subassembly is adapted andconfigured for sliding engagement with the shaft. In a further feature,the upper bearing subassembly includes a pair of mating bushing blockssurrounding the shaft for sliding engagement therewith. Each bushingblock has a groove formed therein for slidingly receiving the shaft. Thegrooves of the bushing blocks are mounted in opposed relation one to theother with the shaft disposed therebetween when the bushing block aremated one with the other. Additionally, the groove formed in eachbushing block is lined with a pad fabricated from a self-lubricatingmaterial. Further still, the pad has longitudinal ribs formed therein.In yet a further feature, the groove formed in each bushing block isgenerally semi-circular.

In another feature, the housing includes a base. The base supports oneof the bearing blocks of the upper bearing subassembly. The shaft ismounted to extend downwardly through the base. Moreover, the base has aslot formed therein along an edge thereof for accommodating the shaft.The slot is configured to permit the shaft to be laterally receivedinto, and laterally removed from, the slot. The slot is substantiallyaligned with the groove of the bearing block supported on the base.

In still another feature, the lower bearing subassembly is adapted andconfigured for rolling engagement with the shaft. Additionally, thehousing includes a base. The lower bearing assembly has at least tworoller assemblies carried below the base at the lower location. Furtherstill, the lower bearing assembly includes at least one mounting memberfor operatively connecting the roller assemblies to at least one of thebase and the upper bearing assembly. In yet an additional feature, thelower bearing assembly has a first mounting member attaching at leastone roller assembly to the base, and a second mounting member attachingat least one roller assembly to the upper bearing assembly. In a stillfurther feature, the upper bearing subassembly includes a pair of matingbushing blocks surrounding the shaft for sliding engagement therewith.The second mounting member is mounted to, and depending downwardly from,one of the bushing blocks.

In an additional feature, the lower bearing assembly has first andsecond roller assemblies supported by the first mounting member, and athird roller assembly supported by the second mounting member. Thefirst, second and third roller assemblies are mounted in surroundingrelation to the shaft.

In yet another aspect of the invention, there is provided areciprocating drive assembly for use in a fluid mixer to impartreciprocating movement along a longitudinal axis to a shaft carrying amixing head for immersion in fluids. The reciprocating drive assemblyincludes a housing, a flywheel, a crank member, a yoke, and first andsecond yoke assemblies. The flywheel is mounted for rotation about arotational axis extending substantially normal to the longitudinal axis.The crank member projects from the flywheel in a direction parallel tothe rotational axis. The yoke is supported by the housing for movementalong a yoke axis disposed substantially parallel to the longitudinalaxis. The yoke is releasably connected to the shaft. The yoke has asubstantially linear race formed therein for receiving the crank member.The race is disposed within the yoke substantially normal to both therotational axis and the yoke axis. The first and second guide assembliesare operatively connected to the housing, and to the yoke for slidingengagement therewith along a pair of guide axes extending substantiallyparallel to the yoke axis. The first and second guide assemblies beinglaterally spaced from each other with the yoke disposed substantiallytherebetween. When the flywheel is rotatively driven, the crank memberis caused to translate linearly within the race thereby urging the yoketo slidingly engage the guide assemblies and move along the yoke axis toeffect longitudinal reciprocating movement of the shaft and the mixinghead.

In an additional feature, each of the first and second guide assembliesis a linear slide assemblies. In still another feature, each linearslide assembly includes a guide rail member associated with at least onecorresponding guide rail following member. Each guide rail member isfixedly mounted to the housing coincident with one of the guide axes.Each of the at least one guide rail following members is rigidlyconnected to the yoke and slidably moveable relative to itscorresponding guide rail member. Further still, each guide rail memberhas upper and lower, spaced-apart, guide rail following membersassociated therewith.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features which are believed to be characteristic of thepresent invention, as to its structure, organization, use and method ofoperation, together with further objectives and advantages thereof, willbe better understood from the following drawings in which a presentlypreferred embodiment of the invention will now be illustrated by way ofexample. It is expressly understood, however, that the drawings are forthe purpose of illustration and description only, and are not intendedas a definition of the limits of the invention. In the accompanyingdrawings:

FIG. 1 is a diagrammatic representation of conventional SXEW processesfor copper extraction.

FIG. 2 is a front, top, right side perspective view of a fluid mixingapparatus according to a preferred embodiment of the present invention,shown operatively mounted on a vessel.

FIG. 3 is a right side cross-sectional view of the fluid mixingapparatus and vessel shown in FIG. 2.

FIG. 4 is a front, top left side perspective view of the fluid mixingapparatus of FIG. 2, showing, inter alia, a reciprocating drive assemblyand mounting means.

FIG. 5 is an exploded perspective view of a portion of the structureshown in FIG. 4.

FIG. 6A is a front elevational view of the structure of FIG. 4, with themixer shaft and shaft gripping means removed for clarity.

FIG. 6B is a view similar to FIG. 6A, with, inter alia, the flywheeldisplaced 90° counter-clockwise relative to its position in FIG. 6A.

FIG. 6C is a view similar to FIG. 6A, with, inter alia, the flywheeldisplaced 90° counter-clockwise relative to its position in FIG. 6B.

FIG. 6D is a view similar to FIG. 6A, with, inter alia, the flywheeldisplaced 90° counter-clockwise relative to its-position in FIG. 6C.

FIG. 7 is a front, top, right side perspective view of the mixing headof the fluid mixing apparatus shown in FIG. 2.

FIG. 8 is a rear, bottom, left side perspective view of the mixing headof the fluid mixing-apparatus shown in FIG. 2.

FIG. 9 is a bottom plan view of the mixing head of the fluid mixingapparatus shown in FIG. 2.

FIG. 10 is a right side elevational view of the mixing head of the fluidmixing apparatus shown in FIG. 2.

FIG. 11 is an enlarged detail view of an alternate embodiment of thesupport webs to that shown in FIG. 7, which view corresponds to the areacircumscribed by circle 11 in FIG. 7.

FIG. 12 is an enlarged detail view of an alternate embodiment of theblade body shown in FIG. 7, which view corresponds to the areacircumscribed by circle 12 in FIG. 7.

FIG. 13 is a view similar to that of FIG. 12, showing a furtheralternate embodiment of the blade body.

FIG. 14 is a front, top, left side perspective view of a fluid mixingapparatus according to the preferred embodiment of the invention in usein a froth flotation cell.

FIG. 15 is a left side cross-sectional view of the structure of FIG. 14.

FIG. 16 a is a side cross-sectional view of an alternate fluid mixingapparatus to that shown in FIG. 3, showing the fluid mixing apparatusmounted within a vessel having baffles disposed therein.

FIG. 16 b is a top left perspective view of the alternate mixing headshown in. FIG. 16 a.

FIG. 16 c is a bottom plan view of the alternate mixing head shown inFIG. 16 a.

FIG. 17 is a partially exploded view showing an alternate mounting meansand an alternate shaft gripping means to those shown in FIG. 4.

FIG. 18 is a sectional view, along sight line 18-18 of FIG. 17, with theapparatus shown fully assembled.

FIG. 19 is a perspective view of yet another alternate mounting meansand an alternate reciprocating drive assembly to those shown in FIG. 4.

FIG. 20 is a partially exploded perspective view of the mounting meansand the reciprocating drive assembly of FIG. 19.

FIG. 21 is a top, right perspective view of an alternate reciprocatingdrive assembly to that shown in FIG. 19.

FIG. 22 is an partially exploded perspective view of the reciprocatingdrive assembly of FIG. 21.

FIG. 23 is a top, right perspective view of an alternate reciprocatingdrive assembly to that shown in FIG. 19.

FIG. 24 is a partially exploded perspective view of the reciprocatingdrive assembly of FIG. 23.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to FIG. 2 of the drawings, a fluid mixing apparatus,according to a preferred embodiment of the present invention anddesignated with general reference numeral 100, is shown in use with afluid containing vessel 102 having a contiguous sidewall 104 centeredabout and defining a longitudinal axis A-A. The fluid mixing apparatus100 is mounted to a frame 140 which spans over the vessel 102.

The fluid mixing apparatus 100 includes a mixing head 106 for immersionin the fluids to be mixed; means 108 for mounting the mixing head 106within the vessel 102; and reciprocating means 110 for impartingreciprocating longitudinal (i.e. vertical) movement to the mixing head106.

Referring to FIG. 7, the mixing head 106 includes: a blade body 112formed about a head axis H-H; a generally tubular hub member 114; and aplurality of support webs 116 for connecting the blade body 112 to thehub member 114.

As shown in FIG. 8, the blade body 112 has a first end 120, an opposedsecond end 122 disposed in spaced relation thereto along the head axisH-H, and a passageway 123 extending longitudinally between the first andsecond ends 120 and 122. In the preferred embodiment, the passageway 123tapers uniformly from the first end 120 to the second end 122 to imparta substantially frustoconical shape to the blade body 112.

The blade body 112 also has an inner surface 126 and an outer surface128. The outer surface 128 defines an inside blade diameter ID at thesecond end 122 of the blade body 112, and an outside blade diameter ODat the first end 120 thereof. The actual outside diameter OD may bebetween 25 and 40 percent of the internal diameter D of the vessel.

The taper in the passageway 123 can be expressed as an angle α, whereangle α is the angle formed between a pair of axes X,X and Y,Y definedby, and coincident with, the intersections of the outer surface 128 ofthe blade body 112 and a plane P-P coincident with the head axis H-H, asshown in as indicated in FIGS. 9 and 10. The angle α is greater than orequal to 90° and less than 180°. Preferably, the angle α is between 90°and 120°.

Whereas in the preferred embodiment, the passageway 123 tapers uniformlyalong its length from the first end 120 to the second end 122 to definea substantially frustoconical blade body 112, the passageway may beconfigured to define other blade body shapes. For instance, thepassageway can be configured to have different rates of tapertherealong. In an alternate embodiment shown in FIGS. 16 a, 16 b and 16c, there is shown a mixing head 400 having a blade body 402. The bladebody 402 includes a first end 404, a second end 406 and a passageway 408defined therebetween. The passageway 408 tapers in a non-uniform fashionbetween the first end 404 and the second end 406. More specifically, theblade body 402 is formed with a point of inflection 410 therein locatedbetween the first end 404 and the second end 406. The passageway 408tapers at first rate from the first end 404 to the point of inflection410, and at a second rate from the point of inflection 410 to the secondend 406. In the alternate embodiment shown, the first rate of taper isless than the second rate of taper. However, this need not be the casein all instances. In some applications, it may be desirable for thefirst rate of taper to be greater than the second rate of taper.

In the preferred embodiment, the blade body 112 is constructed from sixarcuate segments 118 arranged end-to-end. The segments are secured toone another by bolts (not shown) fastened through flanges 124 providedat the ends of each segment 118 for this purpose (see FIGS. 7, 8 and 9).

The hub member 114 is disposed generally coincident with the head axisH-H. Extending substantially radially in a downwardly canted fashionfrom the hub member 114 is the plurality of support webs 116. Thesupport webs 116 connect the arcuate segments 118 of the blade body 112to the hub member 114. Such connection is effected by rivets or bolts(not shown).

Whereas in the preferred embodiment the blade body 112 and support webs116 are substantially smooth, in an alternative embodiment, one or bothof the blade body and the support webs could be formed with perforationsor dimples. For instance, referring to FIG. 12, there is shown analternate blade body 412 having formed therein a plurality ofperforations 414 each extending between an inner surface 416 and anouter surface 418 thereof.

FIG. 13 shows a blade portion 420 provided with a plurality of dimples422 projecting outwardly from an outer surface 424 of the blade portion420 and inwardly from an inner surface 426 of the blade portion 420.This allows fine tuning of the mixing device in a manner not taught bythe prior art.

In yet another alternate embodiment shown in FIG. 11, a support web 430is provided with a plurality of perforations 432, as well as a pluralityof tabs 434 each substantially overlying a respective perforation 432.The tabs 434 are connected to the support web 430 at one edge of saidrespective perforation 432 to form a gill. In this manner, thecharacteristics of the mixing currents produced by the blade body inmotion can be finely tuned to control the droplet size of thedispersion, and hence, the mixing efficiency of the device, whichfeature is not available in prior art mixers.

Referring now to FIG. 3, the preferred mounting means 108 will be seento include a mixer shaft 130 for carrying the mixing head 106 and alinear bearing 132 adapted to slidingly engage the mixer shaft 130.

The mixer shaft 130 has a bottom end 134 releasably mounted to themixing head 106, and a top end 136 operatively connected to thereciprocating means 110. The releasable connection of the mixer shaft130 to the mixing head 106 may be effected by threadingly engaging thebottom end 134 of the mixer shaft 130 with the threaded interior of thehub member 114. When mounted to the mixing head 106, the mixer shaft 130extends substantially coincident with the head axis H-H.

In the preferred embodiment shown in FIGS. 2 and 3, the mixing head 106is mounted to the mixer shaft 130 with the second end 122 of the bladebody 112 being carried below the first end 120 thereof. In an alternateembodiment, the orientation of the mixing head could be reversed suchthat the first end of the blade body is carried below the second tubeend thereof.

As best shown in FIG. 5, the mixer shaft 130 is preferably hollow and isconstructed of a plurality of tube segments 170, threaded at their endsand joined to one-another in end-to-end relation by threaded couplings172, so that segments 170 can be added or removed as desired toaccommodate for different depths of the vessel. The use of a hollowmixer shaft leads to reduced energy consumption by the fluid mixingapparatus during use. In contrast, conventional rotary-type mixers useheavy, solid shafts requiring greater energy input.

The linear bearing 132 is a sleeve-type bearing mounted in surroundingrelation to the mixer shaft 130 for sliding engagement therewith duringits reciprocating longitudinal movement. The linear bearing 132 issecurely fixed to a housing 138 supporting the reciprocating means 110.

As best illustrated in FIG. 4, the reciprocating means 110 includes ashaft gripping means 142 for gripping the mixer shaft 130 adjacent itstop end 136 and a reciprocating drive assembly 144 operatively connectedto the mixing shaft 130 to impart reciprocating longitudinal movement tothe mixing head 106.

With reference to FIGS. 4 and 5, the shaft gripping means 142 preferablyincludes a clamp 163 formed by a pair of mating clamping blocks 164 aand 164 b. Each clamping block 164 a, 164 b has a groove 166 formedtherein which is sized and adapted for receiving the mixer shaft 130 inclose fitting relation thereto. In the preferred embodiment, the groove166 is generally concave and has a semi-circular cross-section. When theclamping blocks 164 a and 164 b are mated, the grooves 166 thereof aredisposed in opposed relation to each other to grippingly receive themixer shaft 130 and captively retain the mixer shaft 130 therebetween.Bolts 168 rigidly fasten the clamping blocks 164 a and 164 b to eachother and to the reciprocating drive assembly 144. Thus fastened, theclamping blocks 164 a and 164 b transfer the reciprocating longitudinalmovement of the reciprocating drive assembly 144 to the mixer shaft 130when the fluid mixing apparatus 100 is in use.

This clamp arrangement permits the relative depth of the mixing head 106in the vessel 102 to be conveniently adjusted from above; the clamp 163need only be loosed, by disengaging the associated bolts 168, whereuponmixer shaft 130 can be raised or lowered as desired, and bolts 168re-engaged.

As shown in FIGS. 4 and 5, the reciprocating drive assembly 144includes: a flywheel 146; a drive 148 for driving rotation of theflywheel 146; a crank member 150 projecting from the flywheel; a yoke152 adapted and configured to receive the crank member 150 therewithin;and guide means 156 for guiding the yoke 152 along a yoke axis 153 forreciprocating longitudinal movement. The flywheel 146, the drive 148,the crank member 150, the yoke 152 and the guide means 156 areoperatively connected to, and co-operate with, each other to form ascotch yoke assembly 143.

The flywheel 146 is mounted to the housing 138 for rotation about arotational axis R-R which is substantially normal to the longitudinalaxis A-A. The drive 148 in the nature of an electric motor, isoperatively connected by its drive shaft (not shown) to the flywheel 146for driving rotation.

Projecting from the flywheel in a direction parallel to the rotationalaxis, is the crank member 150. The crank member 150 is removeablyattached to the flywheel 146 for rotation therewith. For the purpose ofminimizing friction, the crank member 150 includes an inner axle portion182 which is fixedly connected to the flywheel 146 and an outer rollerportion 184 which is rotatably mounted by bearings (not shown) on theinner axle portion 182 (see FIG. 5).

The yoke 152 is mounted within the housing 138 for movement along a yokeaxis 153 disposed substantially parallel to the longitudinal axis A-A.The yoke 152 is displaced from the flywheel 146 in the direction of thecrank member 150 and has formed therein a substantially linear race 154for receiving the crank member 150. The race 154 is disposed within theyoke 152, substantially normal to both the rotational axis R-R and theyoke axis 153. The race 154 is adapted and configured to allowtranslational movement of the crank member 150 relative to the yoke 152as the flywheel 146 rotates.

The guide means 156 includes upper and lower threaded guide shafts 158 aand 158 b which are received in threaded, coaxial bores 156 disposed onupper and lower surfaces of the yoke 152. Corresponding upper and lowerguide bearings 160 a and 160 b are provided on the housing 138 forslidingly engaging the upper and lower guide shafts 158 a and 158 b,respectively. During the reciprocating longitudinal movement, the upperguide shaft 158 a extends protrudes through an aperture (not shown)formed in the housing about which the upper guide bearing 160 a ismounted.

To counter stresses created on the yoke 152 by virtue of its carriage ofthe shaft gripping means 142, the guide means 156 additionally include abalancing or stabilizing shaft 174 and a pair of mating linear bearingblocks 176 a and 176 b fixed to the yoke for sliding engagement with thestabilizing shaft 174. The stabilizing shaft 174 is rigidly connected tothe housing 138 and extends substantially parallel to yoke axis 153.Each linear bearing block 176 a and 176 b has a groove 178 ofsemi-circular cross-section formed therein which is sheathed with aself-lubricating material such as polytetrafluorethylene. When thelinear bearing blocks 176 a and 176 b are mated, the grooves 178 thereofare mounted in opposed relation one with the other with the stabilizingshaft 174 extending longitudinally therebetween. Bolts 180 fasten thelinear bearing blocks 176 a and 176 b to the yoke 152.

The workings of the reciprocating drive assembly 144 are now explainedin greater detail below. With the yoke 152 operatively mounted with theupper and lower guide shafts 158 a and 158 b disposed within the guidebearings 160 a and 160 b, the yoke 152 is mounted to the housing 138 ina manner which constrains movement of yoke 152 otherwise than along theyoke axis 153 and normal to the rotational axis R-R. When the flywheelis rotatively driven by the drive 148, the crank member 150 is caused totranslate linearly within the race 154 thereby urging the yoke 152 tomove along the yoke axis 153 to effect longitudinal reciprocatingmovement of the mixer shaft 130, as indicated by the sequence of FIGS.6A-6D. In the result, the mixing head 106 carried by the mixer shaft 130is longitudinally displaced through a stroke length “S” with a duration“T” for each cycle (where “S” is expressed in inches and “T” isexpressed in minutes). For the sake clarity, a cycle consists of theupstroke and downstroke movement of the mixing head 106. In FIG. 3, themixing head 106 is shown in blackline in a starting position, and inphantom outline, at a position longitudinally displaced from thestarting position through the stroke length “S”.

The length of the resultant stroke may be selected by suitableadjustment to the radial position of the crank member 150 (that is, thedistance between the crank member 150 and the rotation axis R-R).Accordingly, the flywheel 146 is provided with a plurality of threadedsockets 162 disposed in a radial array on the face of the flywheel 146(see FIG. 5). Each threaded socket 162 is sized and adapted to receivethe crank member 150 therein.

Each crank member and socket combination corresponds to a predeterminedstroke length “S”. The duration “T” of each cycle may be selected bysuitable adjustment of the rotational speed of the drive 148.

By virtue of the reciprocating longitudinal movement imparted to themixing head 106, a portion of the fluids in the vessel 102 is urged toflow through the passageway 123 defined in the blade body 112 therebyencouraging efficient mixing of the fluids in the vessel 102. It hasbeen found that mixing efficiencies tend to be improved when the fluidmixing apparatus 100 is operated within a set of operational parametersdefined by the equation:80≲0.36×OD ² /ID ² ×S/T≲550,where:

-   -   OD is the outside diameter of the blade body 112 at the first        end 120 thereof measured in inches;    -   ID is the inside diameter of the blade body 112 at the second        end 122 thereof measured in inches;    -   S is the stroke length measured in inches; and    -   T is the duration of each cycle measured in minutes.

While the stroke length “S” can measure between 2 inches and 24 inches,it is preferred that the stroke length “S” be between 4 inches and 16inches. More preferably, the stroke length “S” is between 8 inches and12 inches.

Moreover, while it has been found that improved mixing efficiencies maybe obtained where the value for OD:ID is greater than 1.0 and less thanor equal to 1.7, preferably, the value for OD:ID lies between 1.5 and1.7.

When operated within the set of operational parameters defined above, ithas been found that the present invention can be used to great advantageas a mixer for a vessel in a solvent extractor unit, as shown in FIGS. 2and 3 and illustrated in Examples 1 and 2 below.

EXAMPLE 1

In the known application of the SXEW process previously described,samples were taken from the outfall of each of the primary vessel;secondary vessel; tertiary vessel and settling tank of a respectivesecondary extraction unit (A) and permitted to separate.

In a parallel secondary extraction unit (B) (ie processing a pregnantleachate of substantially identical composition), a mixing apparatus inaccordance with the present invention (OD=60; ID=40; α=120; S=10;T=0.0333, driven by a 2 hp motor) was substituted for the rotary mixerin the secondary mixing vessel, and samples were again taken from theoutfall from each of the primary, second and tertiary mixing vessels,and from the settling tank, and permitted to separate.

Copper concentration (g/l) was measured in the organic component of eachsample, as follows:

(A) (B) 30 cpm Cu (g/l) Cu (g/l) Primary mixing 2.01 2.01 vesselSecondary mixing 2.06 2.06 vessel Tertiary mixing 2.12 2.13 vesselSettling tank 2.14 2.13

As would be expected, copper concentration from the primary mixingvessel in each of the A and B lines is similar (because to that point inthe process, mixing is provided by identical rotary mixers). However,unexpectedly, copper concentrations in the outfall from the secondarymixers also remained identical, and copper concentration in the outfallfrom the settling tanks remained quite similar, despite the almost 70%reduction in energy input (1.25 hp drawn from a 2 hp drive motor for thereciprocating mixer, as compared to 5.0 hp drawn from the 7.5 hp motordrive for the rotary mixer).

EXAMPLE 2

In a second test, the B line of Example 1 was modified by altering themotor speed of the mixer of the present invention, such that it operatedat 45 cycles/minute (T=0.0222).

Copper concentration (g/l) was again measured, as follows:

(B) [45 cpm] Cu (g/l) Primary mixing 2.00 vessel Secondary mixing 2.08vessel Tertiary mixing 2.11 vessel Settling tank 2.16

Again, as would be expected, copper concentration from the primarymixing vessel in the B line remained similar to that obtained in the Aline (because to that point in the process, mixing is provided byidentical rotary mixers). However, unexpectedly, copper concentrationsin the outfall from the settling tank from the modified B line showedsignificant improvement over the A line results (copper recoveryimproved from 2.14 g/l to 2.16 g/l).

Without intending to be bound by theory, it is believed the fluid mixingapparatus of the present invention provides mixing currents which [atleast in the context of the liquids utilized in SXEW copper extraction]create a dispersion characterized by consistent-sized droplets,uniformly distributed throughout the mixing vessel, whereas in a rotarymixer, there is a wide variation in drop sizes, and in the distributionof said drops, (perhaps due to the fact that the blade in a rotary mixermoves at different speeds along its length). This uniform dispersion isbelieved to provide an environment amenable to efficient mass transferbetween phases, while at the same time providing for substantialdisengagement of the mixed phases within a relatively short time frame.

Whereas the illustrations depict an embodiment of the present inventionwhich is preferred, various modifications are contemplated and describedbelow.

In the preferred embodiment, the shaft gripping means 142 is adapted toallow the clamping blocks 164 a and 164 b to be uncoupled from eachother and detached from the yoke 152 by merely removing the bolts 168.It will be appreciated, however, that in some instances it may not bedesirable to completely detach the clamp from the yoke when releasingthe mixer shaft. In such instances, it would be preferable to uncouplethe clamping blocks while still maintaining a rigid connection betweenone of the clamping blocks and the yoke. In the alternate embodimentshown in FIGS. 17 and 18, this is achieved by replacing clamp 163 with amodified clamp 186. While the clamp 186 is generally similar to theclamp 163 in that it has a pair of mating clamping blocks 188 a and 188b formed with concave grooves 190 therein, it differs in one materialrespect, that is, the clamping block 188 a is fastened to the yoke 152by bolts 192, independently of clamping block 186. Mating of theclamping blocks 188 a and 188 b is achieved by fastening bolts 194.

While in the preferred embodiment the mounting means 108 includes asingle linear bearing 132 which slidingly engages the mixer shaft 130 ata single location, in an alternate embodiment a linear bearing assemblycould be provided for sliding engagement with the mixer shaft at morethan one location. One such alternate embodiment is shown in FIGS. 17and 18, where a mixer shaft designated with reference numeral 196 and alinear bearing assembly is designated with reference numeral 200. Thelinear bearing assembly 200 includes an upper bearing subassembly 202and a lower bearing subassembly 204 for engagement with the mixer shaft196 at respective upper and lower, longitudinally spaced, locations 206and 208, respectively.

The upper bearing subassembly 202 is adapted and configured for slidingengagement with the mixer shaft 196. More specifically, it has a bushing210 formed of mating bushing blocks 212 a and 212 b disposed insurrounding relation to the mixer shaft 196. Each bushing block 212 a,212 b has a concave groove 214 of semi-circular cross-section formedtherein for receiving the mixer shaft 196. Each groove 214 is sheathedor lined with an arcuate pad 216 of self-lubricating material such aspolytetrafluorethylene. Preferably, each pad 216 is ribbed. When thebushing blocks 212 a and 212 b are mated, the grooves 214 thereof aremounted in opposed relation one with the other with the mixer shaft 196extending longitudinally therebetween. The bushing blocks 212 a and 212b are securely attached to each other by bolts 218. The bushing 210 isoperatively connected to the housing 138 by securely mounting bushingblock 212 a to a base 207 of the housing 138.

The lower bearing subassembly 204 is adapted and configured for rollingengagement with the mixer shaft 196. The lower bearing subassembly 204includes at least two roller assemblies identified generally as 220,carried below the base 207 of the housing 138 at the lower location 208.However, preferably, the lower bearing subassembly 204 has first, secondand third roller assemblies respectively, 222, 224 and 226, mounted insurrounding relation to the mixer shaft 196. A first mounting member inthe nature of tubular support 228 attaches the first and second rollerassemblies 222 and 224 to the base 207 of the housing 138. The tubularsupport 228 depends downwardly from the base 207 and terminates at itsdistal end with a flange member 230. The flange member 230 has a pair ofupstanding brackets 232 to which are fastened the first and secondroller assemblies 222 and 224 by bolts 234.

The lower bearing subassembly 204 also includes a second mounting memberin the nature of a pair of removable supports 236. The removablesupports 236 are securely attached to the bushing block 212 a and dependdownwardly therefrom to a terminus 238. The terminus has a bracket 240which extends downwardly therefrom. The third roller assembly is securedto the bracket 240 by bolts 242.

In the preferred embodiment, each roller assembly 222, 224 and 226includes a single roller 239 rotatively mounted to a roller housing 241.It will be appreciated that in alternate embodiments multiple rollersmay be employed.

When the bushing blocks 212 a and 212 b are operably secured to eachother, the first, second and third roller assemblies 222, 224 and 226circumferentially surround the mixer shaft 196, as shown in FIG. 18, ata position beneath and longitudinally spaced from bushing 210. Thesupport provided by the first, second and third roller assemblies 222,224 and 226 at the lower location 208 tends to limit flexure of themixer shaft 196, while permitting reciprocating longitudinal movementthereof.

As best shown in FIG. 17, the mixer shaft 196 can be removed from thehousing 138 for servicing, maintenance, repair or replacement by firstdisassembling the upper bearing subassembly 202 and then by disengagingthe clamp 186. The removal of bolts 218 in bushing 210 allows thebushing block 212 b and the third roller assembly 226 attached thereto,to be removed from sliding engagement with the mixer shaft 196. Bolts194 can then be removed from clamp 186 thereby releasing the mixer shaft196. An open-ended rebate or slot 244 formed along an outermost edge ofthe base 207 permits the mixer shaft 196 to be displaced laterally fromthe base for ease of removal. To further facilitate handling of themixer shaft 196 once released, the mixer shaft 196 is formed with anupper enlarged end portion 246, in which is provided a threaded bore248, to receive a threaded lifting lug (not shown).

With reference to FIGS. 19 and 20, there is shown an alternate mountingmeans 250 and an alternate reciprocating drive assembly 252. Themounting means 250 generally resembles the mounting 108 in that itincludes a mixer shaft 254 and a linear bearing 256. The mixer shaft 254is generally similar to mixer shaft 130, but differs in that it has anenlarged shaft head 258 provided with a support flange 259. Whenoperatively connected to the shaft gripping clamp 260, the supportflange 259 of the mixer shaft 254 abuts clamping blocks 262 and 264thereby providing an additional mechanical connection to the frictionalconnection effected by the clamping blocks 262 and 264.

The linear bearing assembly 256 includes a sleeve-type linear plainbearing 266 mounted in surrounding relation to the mixer shaft 254. Theplain bearing 266 is secured to the base 207 of the housing 138 byfasteners 268. A keyhole-shaped slot 270 formed along an outermost edgeof the base 207 permits the mixer shaft 254 to be displaced laterallyfrom the base 207 during removal thereof. By virtue of the use of theplain bearing 266, it will however be evident that, in order to removethe mixer shaft 244, the plain bearing 266 must first be detached fromthe housing 138, by removing fasteners 268.

The reciprocating drive assembly 252 is generally similar to thereciprocating drive assembly 144 described above in that it has aflywheel 272, a drive 274, a crank member 276, a yoke 278 and guidemeans 280 operatively connected to form a scotch yoke assembly 282.However, whereas guide means 156 of reciprocating drive assembly 144includes upper and lower guide shafts 158 a and 158 b, correspondingupper and lower guide bearings 160 a and 160 b and a single stabilizingshaft 174 with mating linear bearing blocks 176 a and 176 b, the guidemeans 280 employs a pair of parallel left and right guide assemblies inthe nature of first and second linear slide assemblies 284 and 286. Thefirst and second linear slide assemblies 284 and 286 are operativelyconnected to the housing 138 and to the yoke 278 for sliding engagementtherewith along a pair of guide axes 288 and 290 extending substantiallyparallel to a yoke axis designated as 292. The first and second linearslide assemblies 284 and 286 are laterally spaced from each other withthe yoke 278 substantially disposed therebetween.

Each linear slide assembly 284, 286 includes a guide rail member in thenature of a track 294 associated with at least one corresponding guiderail following member in the nature of a saddle member 296. Each track294 is fixedly secured to a support member 298 of the housing 138coincident with a respective guide axis 288 or 290, as the case may be.Each saddle member 296 is adapted and configured for sliding motionalong its corresponding track 294.

The linear slide assemblies 284 and 286 are additionally provided withsaddle mounting members 300 for attaching the saddle members 296 to theyoke 278. The saddle mounting members 300 are generally T-shaped membersmounted between a pair of transverse yoke beams 301 and 303 to define arace 306 formed in the yoke 278. The saddle members 296 are in turnmounted to the back of the saddle mounting members 300 in opposedrelation to the track 294. Thus attached, the saddle members 296 boundon either side the race 306. Looking into the direction of arrow 307(shown in FIG. 19), it can be seen that the linear bearing assemblies284 and 286 are located aft of the yoke 278.

In the alternate embodiment shown and described above, each linear slideassembly 284, 286 is provided with two, longitudinally-spaced, saddlemembers 296 for improved stability; an upper saddle member 308 and alower saddle member 310.

It will be appreciated that other alternative track and saddle memberarrangements may be constructed. Referring to FIGS. 21 and 22, there isshown an alternative reciprocating drive assembly 350 generally similarto reciprocating drive assembly 252. The reciprocating drive assembly350 has, inter alia, a yoke 352 and track-and-saddle type, linear slideassemblies 354 and 356. The linear slide assemblies 354 and 356 aregenerally similar to the linear slide assemblies 284 and 286 in thateach assembly 354, 356 includes a track 358 associated with at least onecorresponding saddle member 360. However, the assemblies 354 and 356differ in that they are fabricated with the saddle members 360 alreadycaptively retained on the tracks 358 for sliding engagement therewith.The yoke 352 differs from yoke 278 shown in FIGS. 19 and 20 in that itis of unitary construction and has saddle mounting portions 362incorporated therein.

Alternate configurations of a reciprocating drive assembly having duallinear slide assemblies, are also possible. Referring now to FIGS. 23and 24, there is shown a reciprocating drive assembly 312 generallysimilar to the reciprocating drive assembly 252 described above. Thereciprocating drive assembly 312 includes a flywheel 314, a drive 316, acrank member 318, a yoke 320 and guide means 322 operatively connectedto form a scotch yoke assembly 324. The guide means 322 is similar tothe guide means 280 in that it also uses a pair of parallel,longitudinally extending, left and right guide assemblies. However,whereas the guide means 280 employs a pair of tracks 294 each associatedwith at least one saddle member 296, the guide means 322 uses a Thompsonshaft arrangement, that is, a pair of guide posts 326 each associatedwith at least one linear sliding block 328.

Each guide post 326 is mounted within the housing 138 to extend upwardlybetween the base 207 and a top plate 332 thereof. The guide posts 326are secured to the base 207 by collar members 330 and fasteners (notshown). Each linear sliding block 328 is mounted in surrounding relationto its associated guide post 326 for sliding engagement therewith. Aswith the linear assemblies 284 and 286, the mounting members 333 attachthe linear sliding blocks 328 with the yoke 320. However, in thisembodiment, the linear slide assemblies (consisting of guide posts 326and linear sliding blocks 328) are located fore of the yoke 320.

While the reciprocating drive assembly 318 operates in a generallysimilar fashion to the reciprocating drive assembly 252, the manner inwhich the flywheel 314, the crank member 318 and the yoke 320 co-operatewith each other differs. Unlike crank member 276, the crank member 318does not have an inner axle fixedly connected to the flywheel with anouter roller portion rotatably mounted thereon. The crank member 318 isembodied in a cam follower block 334 adapted and configured for slidingmovement within the race 335 defined in the yoke 320. The cam followerblock 334 is preferably made of steel and houses therein a rollerbearing 336 and an axle 338 rotatively mounted to the roller bearing336. The axle 338 is received in socket 340 formed in the flywheel 314.Brass wear plates 342 are fastened to the top and bottom surfaces of thecam follower block 334 for improved wear resistance. When the camfollower 334 is mounted within the race 336, the brass wear plates 342bear against hard steel wear plates (not shown) lining the race 335.

While in the preferred embodiment, a scotch yoke apparatus is utilizedto provide linear reciprocating movement, it will be evident that othermechanisms, such as crank shafts, cam and cam follower mechanisms, andswash plates are possible substituents therefor.

Of course, whereas the detailed description herein pertains specificallyto the recovery of copper from copper bearing ores, it should also beunderstood that the present invention may be utilized in otherapplications wherein SXEW processes are utilized, such as, for example,in the recovery of zinc, nickel, platinum, uranium and gold.

Moreover, it will be evident that the invention may have advantageousutility even outside the SXEW process, in other mixing applications,such as in the context of a froth flotation cell, illustrated in FIGS.14 and 15, wherein the fluid mixing apparatus is used to agitate aslurry to form a froth, and a paddle mechanism 32 is operatively mountedto the vessel 102 to scour froths produced thereby.

As shown in FIG. 16 a, the fluid mixing apparatus can also be employedin a vessel having baffles 500 disposed therein.

It will, of course, also be understood that various other modificationsand alterations may be used in the design and manufacture of the mixingapparatus according to the present invention without departing from itsspirit and scope. Accordingly, the scope of the present invention shouldbe understood as limited only by the accompanying claims, purposivelyconstrued.

1. An apparatus for mixing fluids within a vessel having a contiguoussidewall centered about and defining a longitudinal axis, the mixingapparatus comprising: a mixing head having a blade body for immersion inthe fluids, the blade body having a first end, an opposed second enddisposed in spaced relation thereto along a blade body axis, and apassageway extending therealong between the first and second ends; thepassageway tapering from the first end to the second end; the blade bodyfurther having an inner surface and an outer surface, the outer surfaceof the blade body defining an inside blade diameter ID at the secondend, and an outside blade diameter OD at the first end; means formounting the mixing head within the vessel; and means for impartingreciprocating longitudinal movement to the mixing head, thereciprocating longitudinal movement being defined by a stroke length S,with a duration T for each cycle, the mixing apparatus being operablewithin a set of operational parameters defined by the equation:80≦˜0.36×OD ² /ID ² ×S/T≦˜550, where OD, ID and S are each expressed ininches, and T is expressed in minutes; and wherein by virtue of thereciprocating longitudinal movement imparted to the mixing head, aportion of the fluids is urged to flow through the passageway defined inthe blade body to thereby encourage efficient mixing of the fluids inthe vessel.
 2. A mixing apparatus according to claim 1, wherein thestroke length S is between 2 inches and 24 inches.
 3. A mixing apparatusaccording to claim 2, wherein the stroke length S is between 4 inchesand 16 inches.
 4. A mixing apparatus according to claim 3, wherein thestroke length S is between 8 inches and 12 inches.
 5. A mixing apparatusaccording to claim 1, wherein the OD:ID is greater than 1.0 and lessthan or equal to 1.7.
 6. A mixing apparatus according to claim 5,wherein the OD:ID is between 1.5 and 1.7.
 7. A mixing apparatusaccording to claim 1, wherein the stroke length S is between 8 and 12inches; and the OD:ID is between 1.5 and 1.7.
 8. An apparatus for mixingfluids within a vessel having a contiguous sidewall centered about anddefining a longitudinal axis, the mixing apparatus comprising: a housingpositionable above said vessel; a mixing head having a blade body forimmersion in the fluids, the blade body having a first open end, anopposed second open end disposed in spaced relation thereto along ablade body axis, and a passageway extending therealong between the firstand second open ends; the passageway tapering from the first open end tothe second open end; a shaft for supporting the mixing head extendinginto the vessel; a reciprocating drive assembly positioned substantiallywithin the housing, the reciprocating drive assembly being operativelyconnected to the shaft to impart reciprocating longitudinal movement tothe mixing head; and a linear bearing assembly mounted to the housing insurrounding relation to the shaft, the linear bearing assembly includingupper and lower bearing subassemblies for engagement with the shaft atrespective upper and lower, longitudinally spaced, locations.
 9. Amixing apparatus according to claim 8, wherein the upper bearingsubassembly is adapted and configured for sliding engagement with theshaft.
 10. A mixing apparatus according to claim 9, wherein the upperbearing subassembly includes a pair of mating bushing blocks surroundingthe shaft for sliding engagement therewith, each bushing block having agroove formed therein for slidingly receiving the shaft, the grooves of,the bushing blocks being mounted in opposed relation one to the otherwith the shaft disposed therebetween when the bushing block are matedone with the other.
 11. A mixing apparatus according to claim 10,wherein the groove formed in each bushing block is lined with a padfabricated from a self-lubricating material.
 12. A mixing apparatusaccording to claim 11, wherein the pad has longitudinal ribs formedtherein.
 13. A mixing apparatus according to claim 10, wherein thegroove formed in each bushing block is generally semi-circular.
 14. Amixing apparatus according to claim 10, wherein: the housing includes abase, the base supporting one of the bearing blocks of the upper bearingsubassembly; and the shaft is mounted to extend downwardly through thebase.
 15. A mixing apparatus according to claim 14, wherein the base hasa slot formed therein along an edge thereof for accommodating the shaft,the slot being configured to permit the shaft to be laterally receivedinto, and laterally removed from, the slot; the slot being substantiallyaligned with the groove of the bearing block supported on the base. 16.A mixing apparatus according to claim 8, wherein the lower bearingsubassembly is adapted and configured for rolling engagement with theshaft.
 17. A mixing apparatus according to claim 16, wherein: thehousing includes a base; and the lower bearing assembly has at least tworoller assemblies carried below the base at the lower location.
 18. Amixing apparatus according to claim 17, wherein the lower bearingassembly includes at least one mounting member for operativelyconnecting the roller assemblies to at least one of the base and theupper bearing assembly.
 19. A mixing apparatus according to claim 18,wherein the lower bearing assembly has a first mounting member attachingat least one roller assembly to the base, and a second mounting memberattaching at least one roller assembly to the upper bearing assembly.20. A mixing apparatus according to claim 19, wherein the first mountingmember is mounted to, and depends downwardly from, the base.
 21. Amixing apparatus according to claim 19, wherein: the upper bearingsubassembly includes a pair of mating bushing blocks surrounding theshaft for sliding engagement therewith; the second mounting membermounted to, and depending downwardly from, one of the bushing blocks.22. A mixing apparatus according to claim 21, wherein the lower bearingassembly has first and second roller assemblies supported by the firstmounting member, and a third roller assembly supported by the secondmounting member; the first, second and third roller assemblies beingmounted in surrounding relation to the shaft.
 23. A mixing apparatusaccording to claim 16, wherein the lower bearing assembly has first,second and third roller assemblies mounted in surrounding relation tothe shaft.